Effects of aluminium addition and austempering temperatures on Al-alloyed ductile iron microstructure and mechanical properties

The research investigates the effect of varying amounts of aluminium (1.05, 1.575, 2.29, 3.02 and 3.74 wt.%) addition and heat treatment (austempering at 300, 350, 400 oC) on the microstructure and mechanical properties of ductile cast iron alloys. The graphitizing effects of the Al alloy and varied austempering temperatures on hardness, tensile strength, and impact toughness of the ductile cast iron (DCI) were evaluated. The results of the influences of Al addition and heat treatment on the properties of the DCI determined were presented as graphical data while the microstructures were done by using a scanning electron microscope (SEM). The microstructures revealed that the addition of Al into the matrix brings about the precipitation of ferrite around the graphite nodules. The combined effects of the increase Al content and austempering temperatures produced greater hardness values on the Al-alloyed DCI samples than the as-cast sample. The hardness value for the entire sample ranged between 27.25 to 57.03 BHN. Tensile strength increased with an increase in Al content and lower austempering temperatures, whereas, the impact toughness increased with an increase in Al content and higher austempering temperature.